Improved monitoring system of neutron flux during boron-neutron capture therapy

Continuous and simultaneous monitoring of neutron flux in the course of a boron-neutron capture operation on a brain tumor has been achieved using a new monitoring system. A silicon surface barrier diode mounted with 6LiF instead of the previously reported borax is used to sense neutrons. The pulse heights of 3H and α particles from 6Li(n, α)2H reaction are sufficiently high and well separated from noises due to γ rays. The effect of pulse-height reduction due to the radiation damage of the diode thus becomes smaller, permitting continuous monitoring. The relative error of the monitoring is within 2% over 5 hr for a neutron-flux density of 2 x 109 n/cm2 sec